/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.hsc.lock.annotation;

import com.hsc.lock.interceptor.LockResolver;
import com.hsc.lock.interceptor.SimpleLockResolver;
import com.hsc.lock.interceptor.key.KeyGenerator;
import com.hsc.lock.store.CacheManager;
import com.hsc.lock.store.LockStore;
import org.springframework.core.annotation.AliasFor;

import java.lang.annotation.*;
import java.util.concurrent.Callable;

/**
 * Annotation indicating that the result of invoking a method (or all methods
 * in a class) can be cached.
 *
 * <p>Each time an advised method is invoked, caching behavior will be applied,
 * checking whether the method has been already invoked for the given arguments.
 * A sensible default simply uses the method parameters to compute the key, but
 * a SpEL expression can be provided via the {@link #key} attribute, or a custom
 * {@link KeyGenerator} implementation can
 * replace the default one (see {@link #keyGenerator}).
 *
 * <p>If no value is found in the cache for the computed key, the target method
 * will be invoked and the returned value stored in the associated cache. Note
 * that Java8's {@code Optional} return types are automatically handled and its
 * content is stored in the cache if present.
 *
 * <p>This annotation may be used as a <em>meta-annotation</em> to create custom
 * <em>composed annotations</em> with attribute overrides.
 *
 * @author Costin Leau
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @author Sam Brannen
 * @see CacheConfig
 * @since 3.1
 */
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Cacheable {

    /**
     * Alias for {@link #cacheNames}.
     */
    @AliasFor("cacheNames")
    String[] value() default {};

    /**
     * Names of the caches in which method invocation results are stored.
     * <p>Names may be used to determine the target cache (or caches), matching
     * the qualifier value or bean name of a specific bean definition.
     *
     * @see #value
     * @see CacheConfig#cacheNames
     * @since 4.2
     */
    @AliasFor("value")
    String[] cacheNames() default {};

    /**
     * Spring Expression Language (SpEL) expression for computing the key dynamically.
     * <p>Default is {@code ""}, meaning all method parameters are considered as a key,
     * unless a custom {@link #keyGenerator} has been configured.
     * <p>The SpEL expression evaluates against a dedicated context that provides the
     * following meta-data:
     * <ul>
     * <li>{@code #root.method}, {@code #root.target}, and {@code #root.caches} for
     * references to the {@link java.lang.reflect.Method method}, target object, and
     * affected cache(s) respectively.</li>
     * <li>Shortcuts for the method name ({@code #root.methodName}) and target class
     * ({@code #root.targetClass}) are also available.
     * <li>Method arguments can be accessed by index. For instance the second argument
     * can be accessed via {@code #root.args[1]}, {@code #p1} or {@code #a1}. Arguments
     * can also be accessed by name if that information is available.</li>
     * </ul>
     */
    String key() default "";

    /**
     * The bean name of the custom {@link KeyGenerator}
     * to use.
     * <p>Mutually exclusive with the {@link #key} attribute.
     *
     * @see CacheConfig#keyGenerator
     */
    String keyGenerator() default "";

    /**
     * The bean name of the custom {@link CacheManager} to use to
     * create a default {@link LockResolver} if none
     * is set already.
     * <p>Mutually exclusive with the {@link #cacheResolver}  attribute.
     *
     * @see SimpleLockResolver
     * @see CacheConfig#cacheManager
     */
    String cacheManager() default "";

    /**
     * The bean name of the custom {@link LockResolver}
     * to use.
     *
     * @see CacheConfig#cacheResolver
     */
    String cacheResolver() default "";

    /**
     * Spring Expression Language (SpEL) expression used for making the method
     * caching conditional.
     * <p>Default is {@code ""}, meaning the method result is always cached.
     * <p>The SpEL expression evaluates against a dedicated context that provides the
     * following meta-data:
     * <ul>
     * <li>{@code #root.method}, {@code #root.target}, and {@code #root.caches} for
     * references to the {@link java.lang.reflect.Method method}, target object, and
     * affected cache(s) respectively.</li>
     * <li>Shortcuts for the method name ({@code #root.methodName}) and target class
     * ({@code #root.targetClass}) are also available.
     * <li>Method arguments can be accessed by index. For instance the second argument
     * can be accessed via {@code #root.args[1]}, {@code #p1} or {@code #a1}. Arguments
     * can also be accessed by name if that information is available.</li>
     * </ul>
     */
    String condition() default "";

    /**
     * Spring Expression Language (SpEL) expression used to veto method caching.
     * <p>Unlike {@link #condition}, this expression is evaluated after the method
     * has been called and can therefore refer to the {@code result}.
     * <p>Default is {@code ""}, meaning that caching is never vetoed.
     * <p>The SpEL expression evaluates against a dedicated context that provides the
     * following meta-data:
     * <ul>
     * <li>{@code #result} for a reference to the result of the method invocation. For
     * supported wrappers such as {@code Optional}, {@code #result} refers to the actual
     * object, not the wrapper</li>
     * <li>{@code #root.method}, {@code #root.target}, and {@code #root.caches} for
     * references to the {@link java.lang.reflect.Method method}, target object, and
     * affected cache(s) respectively.</li>
     * <li>Shortcuts for the method name ({@code #root.methodName}) and target class
     * ({@code #root.targetClass}) are also available.
     * <li>Method arguments can be accessed by index. For instance the second argument
     * can be accessed via {@code #root.args[1]}, {@code #p1} or {@code #a1}. Arguments
     * can also be accessed by name if that information is available.</li>
     * </ul>
     *
     * @since 3.2
     */
    String unless() default "";

    /**
     * Synchronize the invocation of the underlying method if several threads are
     * attempting to load a value for the same key. The synchronization leads to
     * a couple of limitations:
     * <ol>
     * <li>{@link #unless()} is not supported</li>
     * <li>Only one cache may be specified</li>
     * <li>No other cache-related operation can be combined</li>
     * </ol>
     * This is effectively a hint and the actual cache provider that you are
     * using may not support it in a synchronized fashion. Check your provider
     * documentation for more details on the actual semantics.
     *
     * @see LockStore#get(Object, Callable)
     * @since 4.3
     */
    boolean sync() default false;

}
